Andrew P Collins

If you occasionally need to move a ton of small things (or just one very large thing) there are numerous companies who will rent you a trailer. But how can you make sure you won't screw up? I went to U-Haul's test facility in Arizona to learn both the right and wrong way to tow a U-small trailer.

Most rental trailers are plastered in warning decals. I even saw QR codes you could scan on your phone to pull up instructional loading and coupling videos. I thought that was clever, but apparently my view was unique.

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"you know, you might be the first person to notice those. We have them on hundreds of trailers and as far as I know about five have been watched," a U-Haul employee told me when I asked about them.

That's too bad, because there's nothing like a good crash video to motivate you to heed instructions... see below.

Luckily, the rule to remember for safe trailer loading is pretty simple: put 60% of your trailer's weight in the front half of the trailer. That's the actual front half, not just in front of the axle, which I'm told is a common misconception. Some trailer axles are positioned further back from the centerline to increase leverage on the hitch ball and further alleviate "whipping," as we'll discuss below.

The other thing you'll have to keep track of is your tongue weight — the downward force that the coupler from the trailer (called the tongue) puts on the hitch of the tow vehicle.

Every vehicle has a different maximum tongue weight it can bear; look for that in your vehicle's manual.

The consensus among industry experts puts acceptable tongue weight between 9 and 15 percent of the total trailer weight. Hutchinson reckons "about 10%" is optimal, partially because it's an easier number to calculate.

It's possible to measure the tongue weight your trailer is exerting with reasonable precision by simply placing a scale where the hitch ball is meant to go, but there's also an "eyeballer's" method for those of you who hate counting:

With an empty trailer connected to an empty tow vehicle, measure measure the distance from the ground to the top of the spinner on the coupler. That's called the "handwheel" and you tighten it to clamp the coupler on to the hitch ball.

Load the trailer and re-measure the distance from the ground to the top of the handwheel.

Take the unloaded distance and subtract loaded distance.

If the result is 1 inch or more, you're good to go- there's enough tongue weight. If the change was less than 1 inch, reload the trailer and put more weight in the front half.

The end result should be a level trailer. If it's tilted forward, tongue weight is excessive and some cargo must be moved backward of the center line or removed completely.

The trailers I saw at U-Haul's shop had decals indicating exactly where that center line was, along with a little drama to scare you into submission with the words "FAILURE," and "WHIPPING" in caps-lock. A gnarly illustration of a car swerving helplessly ahead of a trailer completed the message. "A powerful visual is important," said Hutchinson. "People don't want that [pointing to picture] happening."

Indeed. But what does this "whipping" feel like, how do we avoid it and what do we do when it happens?

To find out I went to U-Haul's test track in Phoenix, AZ, a for-hire engineering research facility called Exponent. It's an oval loop with banked turns and a giant skid pad.

An improperly balanced trailer can be a ticking timebomb chasing your truck. U-Haul rep and trailer nerd Sperry Hutchinson showed us exactly what can happen when a trailer is loaded incorrectly, and how to make sure your rig doesn't start the truffle shuffle next time you tow.

If you've ever wondered what happens when you lose control of your U-Haul trailer at highway…
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A 2008 Dodge Journey SXT was offered up as the test mule, and some of U-Haul's engineers fitted one of their 1,000-pound-capable motorcycle trailers with "test weights." We ran around the track with the weights loaded correctly; 60% ahead of center, without incident. You can see what happened in the video when the weights were moved to illustrate a "dramatically poor" loading job.

Even a correctly loaded trailer will exhibit some sway in the rear-view mirror, but you should not feel the effects through the steering wheel.

With an off-balanced trailer, the further askew your load is, the lower the speed will be at which you'll feel the effect — imagine The Hulk picking up your vehicle by its rear bumper and shaking it from side to side.

The trailer is acting like a lever; applying a powerful lifting force on the rear of the tow vehicle causing traction to disappear from the back axle throwing weight distribution of the whole rig all over the place.

This phenomenon is aptly referred to as "whipping."

You're obviously not going to see many people slapping 1,000 pounds of mass on the last foot of their trailer. But consider that if the load is close to 60% in front, but not quite there, the action you see in the video takes place at a higher speed, and has a lot more potential to make a mess.

If you do feel the effects of trailer whipping, it's important to remember not to apply brakes. Doing so will take ever more weight off the rear wheels and exacerbate the situation. The only viable escape is to let off the throttle and hold the steering wheel straight-ahead. If and when you get your setup under control, that would be a good time to pull over and re-adjust your load. You might need a change of underwear while you're at it.

I can promise ignoring the brake is going to be tough. It was all fun and games on a closed course, but with family and valuables aboard on a public road, I can see panic setting in plenty quick. You'll just have to try to think about physics; here you need your vehicle's weight, and remember where application of the brakes will direct that weight.

Pulling a trailer that's correctly loaded is straightforward; just be sure to leave yourself a little extra stopping distance as abrupt braking puts strain on the connection between trailer and tow vehicle. It's also important to be aware of any speed restrictions the trailer might have— those tires aren't always stout enough to keep up with higher highway speed limits.

It's recommended that you go down a hill in the same gear you went up it, to maintain maximum control of your speed.

Last but not least; don't forget how much "longer" when moving to pass or round a corner.